close

Вход

Забыли?

вход по аккаунту

?

Synthesis and Reactions of Highly Strained 2 3-Bridged 2H-Azirines.

код для вставкиСкачать
Angewandte
Chemie
Strained Molecules
DOI: 10.1002/anie.200600483
Synthesis and Reactions of Highly Strained
2,3-Bridged 2H-Azirines**
Klaus Banert* and Barbara Meier
Strained compounds are of special interest because of their
increased energy content and the enhanced reactivity that
frequently results from this. The already considerable ring
strain of simple cyclopropenes (ca. 54 kcal mol1) is significantly increased if the three-membered ring is incorporated
into the bicyclic framework 1 (Scheme 1).[1] It should be
possible to transfer this concept from the hydrocarbons 1 to
the heterocycles 3.[2, 3] The 2,3-bridged azirine 3 d, which is
easily obtainable from azide 2 d by photolysis or thermolysis,
can be distilled in vacuo,[4] whereas the more unstable
compound 4 could be characterized only in solution.[5] Until
now, the even more strained azirine 3 b and many similar
bridged azirines bearing a six-membered ring can be generated only in situ and detected by trapping reactions.[4a, 6] Thus,
[*] Prof. Dr. K. Banert, Dr. B. Meier
Lehrstuhl f#r Organische Chemie
Technische Universit+t Chemnitz
Strasse der Nationen 62, 09111 Chemnitz (Germany)
Fax: (+ 49) 371-531-1839
E-mail: klaus.banert@chemie.tu-chemnitz.de
[**] Reactions of Unsaturated Azides, Part 19. This work was supported
by the Fonds der Chemischen Industrie. We thank Dr. M. Hagedorn,
Dr. F. KDhler, and Dr. J. Lehmann for support with spectroscopic
investigations. Part 18: J. R. Fotsing, M. Hagedorn, K. Banert,
Tetrahedron 2005, 61, 8904–8909.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2006, 45, 4015 –4019
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4015
Communications
Scheme 1.
the prospect of spectroscopically characterizing 3 b in solution
appears to be gloomy, especially as the 1H NMR data of the
analogous short-lived hydrocarbon 1 b were obtained even at
90 8C only partially.[7]
We now report the heterocycles 3 b, 3 c, 3 e, 3 f, and 3 h–j
(Table 2), which have been analyzed spectroscopically for the
first time, as well as some further 2,3-bridged azirines. The
highly strained title compounds undergo several addition and
cycloaddition reactions that are not possible for simple 2Hazirines.[2]
To produce the corresponding azirines, we prepared first
the necessary vinyl azides[8] 2 c,[9] 2 d,[4b,c] and 2 e[9] by using
Hassner6s method,[10] that is, by electrophilic addition of
iodine azide, generated in situ, to cycloalkenes followed by
base-induced elimination of hydrogen iodide. In the case of
five- and six-membered rings, it is well-known[4b,c, 11–13] that this
method does not lead to vinyl azides, but rather to allyl azides.
Thus, we switched over to Zbiral6s[11b] sequence for the
synthesis of 2 a and 2 b. Neither route was successful in the
synthesis of 1-azido-2-methylcycloalkenes such as 2 f, 2 g, and
2 h (Scheme 2). The dehydration with thionyl chloride of a
mixture of the regioisomeric azidoalcohols 6[14] and 7,[14]
which could be easily synthesized from the inexpensive
limonene oxide 5, was problematic and led only to a very
low yield of 2 f. However, the formal addition of iodine azide
to 1-methylcycloalkenes 8 g, h assisted by cerium(IV) ammonium nitrate (CAN)[15] and the subsequent treatment of 9 g, h
with potassium tert-butylate gave somewhat better yields of
the desired vinyl azides 2 g, h.
When a solution of the azide 2 b in anhydrous CDCl3 or
[D8]toluene was irradiated at 50 8C with a mercury highpressure lamp, surprisingly the bridgehead azirine 3 b could
be detected even at room temperature by its IR as well as
1
H NMR and 13C NMR data (Table 1).[16] However, a rapid
subsequent reaction led to the formation of the dimer 11 b,
and this product was quickly oxidized to 12 b when oxygen
was not excluded rigorously (Table 2).[17] Addition of tetrachloro-1,4-benzoquinone caused instantaneous transformation of 11 b to 12 b. If photolysis of 2 b is performed in CDCl3
or [D8]toluene saturated with water, the dimerization 3 b!
11 b is accelerated so strongly that the intermediate 3 b can no
longer be observed by NMR spectroscopy. We assume that
even traces of water act as a catalyst and initiate the reaction
sequence shown in Scheme 3. The less strained bridgehead
azirine 3 c dimerizes considerably slower than 3 b (3 months,
4016
www.angewandte.org
Scheme 2.
Table 1: Selected physical data of 2,3-bridged 2H-azirines 3 b and 3 c.[a]
3 b: IR (CDCl3): ñ = 1743 cm1 (C=N); 1H-NMR (CDCl3, 40 8C): d = 1.01
(ddddd, 2J = 14.0, 3J = 9.9, 8.9, 4.7, 2.6 Hz, 1 H, 4-Hendo), 1.28 (ddddd,
2
J = 14.7, 3J = 5.5, 4.7, 4J = 1.1, 3J = 0.6 Hz, 1 H, 5-Hendo), 1.41 (ddddd,
2
J = 14.0, 3J = 7.3, 5.5, 5.0, 2.6 Hz, 1 H, 4-Hexo), 1.54 (dddddd, 2J = 12.6,
7.3, 6.9, 5.0, 2.6, 4J = 1.1 Hz, 1 H, 3-Hendo), 1.64 (dddd, 2J = 14.7, 3J = 8.9,
5.0, 3.8, 1 H, 5-Hexo), 1.82 (ddddd, 2J = 12.6, 3J = 9.9, 7.6, 7.1, 2.6 Hz, 1 H,
3-Hexo), 2.28 (dd, 3J = 3.8, 0.6 Hz, 1 H, 6-H), 2.84 (ddd, 2J = 12.7, 3J = 7.1,
6.9 Hz, 1 H, 2-Hexo), 3.24 ppm (ddd, 2J = 12.7, 3J = 7.6, 5.0 Hz, 1 H, 2Hendo); 13C-NMR (CDCl3, 40 8C): d = 21.39 (t, C-4), 23.85 (t, C-3), 25.96
(d, 1JC,H 192 Hz, C-6), 27.27 (t, C-2), 28.33 (t, C-5), 179.04 ppm (s, C1).
3 c: Colorless liquid; IR (CDCl3): ñ = 1764 cm1 (C=N); 1H NMR (CDCl3):
d = 0.87 (m, 1 H), 1.27 (m, 1 H), 1.41 (m, 1 H), 1.54 (m, 1 H), 1.66–1.76
(m, 3 H), 2.07 (m, 1 H), 2.13 (m, 1 H), 2.79 (m, 1 H, 2-H), 3.00 ppm (m,
1 H, 2-H); 13C NMR (CDCl3): d = 26.37 (t), 27.46 (t), 27.82 (t), 28.02 (t),
28.96 (d, 1JC,H = 183 Hz C-7), 31.53 (t), 175.35 ppm (s, C-1).
[a] The data of the other bridgehead azirines and those of other new
compounds are summarized in the Supporting Information. 1H NMR:
300 MHz, 13C NMR: 75 MHz. The assignment of NMR signals and the
measurement of coupling constants were performed with the help of
1
H,1H double-resonance experiments, 1H NMR NOE difference spectra,
1
H,1H COSY experiments, 13C,1H shift correlations, DEPT135, GATED,
and 2D J-resolved experiments, as well as spectrum simulation in the
case of 3 b. The vicinal coupling constants found for 3 b correlate with the
H-C-C-H torsion angles, which were calculated semiempirically
(MOPAC), with the Karplus relationship.
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 4015 –4019
Angewandte
Chemie
Table 2: Generation and successive reactions of 2,3-bridged 2H-azirines 3.
Yield[a] of 3 [%]
after photolysis
Substrate 2
Yield[a] of 3 [%]
after thermolysis
Yield
Yield[a]
of 11 [%] of 12 [%]
R1
R2
X
2a
5 H
2b
6 H
2c
7 H
2 e[e] 12 H
2f
6 CMe = CH2
2g
5 H
2h
6 H
2i
6 H
2j
6 H
H
H
H
H
Me
Me
Me
H
Me
CH2
0 (CDCl2F, 120 8C)
n.i.[b] n.d.[b]
CH2
83 (CDCl3, 50 8C)
0 (CDCl3, 80 8C)
n.m.[b]
CH2
91 (CDCl3, 50 8C)
85 (CDCl3, 80 8C)
n.d.
CH2
100 (CDCl3, 50 8C)
96 (CDCl3, 80 8C)
0
CH2
94[f ] (CDCl3, 50 8C)
n.i.
n.i.
0 (CD2Cl2, 80 8C)
n.i. 65[c,g,h]
CH2
CH2
85 (CDCl3, 50 8C)
n.i. 52[a,d,i]
C = O 22[j] (CD2Cl2, 80 8C)
n.i.
0
n.i.
0
C = O 65 (CDCl3, 50 8C)
n
45[c]
49[d]
54[d]
0
–
–
–
0
–
[a] Yield based on 1H NMR standard. [b] n.i. = reaction not investigated, n.d. = compound not detected
because of rapid oxidation to 12, n.m. = yield not measured. [c] Yield based on azide 2. [d] Yield based
on azirine 3. [e] Mixture of (Z)-2 e/(E)-2 e = 2.5:1. [f ] 1:1 mixture of diastereomers. [g] Yield based on
isolated products. [h] Mixture of diastereomers (60:40). [i] Mixture of diastereomers (ca. 5:1). [j] 47 % 2 i
was recovered; prolonged irradiation led to destruction of 3 i.
11 g, respectively (Table 2), and we
were able to isolate the nitrile 15 k
as well as the azo compound 16 k
after photolysis of 2 k and workup
by chromatography (Scheme 4).
The diradical intermediates shown
in Scheme 4 could possibly play a
role in the formation of 15 k and
16 k; thus, the difficulties in detecting azirine 3 k by NMR spectroscopy may result not only from its
short lifetime.
As a result of their increased
ring strain, 2,3-bridged azirines
such as 3 b, 3 c, and 3 h can undergo
addition and cycloaddition reactions that are not possible for
simple
2H-azirines.
Whereas
alkyl- or aryl-substituted azirines
do not react with cyclopentadiene,[2b] the corresponding Diels–
Alder reactions of 3 b and 3 c
Scheme 3.
20 8C, 54 % yield of 12 c). Moreover, we were not able to
observe the corresponding reaction of 3 e. The azirines 3 i, j
generated from azides 2 i, j[6f,g] did not form pyrazines
analogous to 11 and 12, but decomposed by unknown
subsequent reactions.
The significantly increased ring strain for 3 b relative to 3 c
is demonstrated by the 1J(13C,1H) NMR coupling constants of
the CH unit at the bridgehead (Scheme 1). Consequently, 3 b
is distinctly more reactive than the azirine 3 c, which can also
be observed, similarly to 3 e, after thermolysis in solution
(Table 2) and which can be isolated after flash vacuum
pyrolysis (300 8C, 2 < 104 Torr) in 78 % yield. In contrast, it
was not possible to remove the solvent from a solution of
photochemically generated 3 b without complete destruction.
Furthermore, no trace of 3 b could be detected by monitoring
the thermolysis of a solution of 2 b in chloroform or
cyclohexane by NMR spectroscopy,[16] whereas flash vacuum
pyrolysis led to low yields of 3 b. Comparison of the properties
of 3 b with those of 3 h and of 3 i with those of 3 j shows that an
additional methyl group at the bridgehead increases the
kinetical stability of the azirines significantly.
Our attempts to detect azirines bridged by a fivemembered ring, such as 3 a, 3 g, or 3 k, by spectroscopy
directly led at best to strongly broadened NMR signals of the
starting materials even after irradiation and measurement at
low temperatures (Table 2 and Scheme 4). Nevertheless, the
photolyzed solutions yielded definite products after thawing.
The azides 2 a and 2 g gave the pyrazine derivatives 12 a and
Angew. Chem. Int. Ed. 2006, 45, 4015 –4019
Scheme 4.
were successful under mild conditions (1 h, 50 8C for 17 b
and 4 days, 20 8C for 17 c, Scheme 5). Of the four imaginable
diastereomeric [4+2] cycloadducts (exo,exo; endo,exo;
exo,endo; endo,endo), we isolated always the exo,endo
stereoisomer 17, which has the cyclopentadiene added to
the exo side of the bridgehead azirine to form a 5-azanorbornene with an attached three-membered ring in the endo
position. The addition of hydrogen cyanide to the highly
strained azirines takes place already at 50 8C and leads to
good yields of the aziridines 18 b, c, h. The less strained 2,3bridged heterocycle 3 e does not undergo addition of hydrogen cyanide even after 7 days at 90 8C.[18] However, the
photolysis of the azide 2 l[19] in the presence of hydrogen
cyanide can be used to gain evidence for the highly strained
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
4017
Communications
(Table 3). These tricyclic compounds, as well as 19 c, could be
characterized by their 1H and 13C NMR data. The analogous
transformations of 3 c or the less reactive azirine 3 d required
1 h at 40 8C and 4 days at 22 8C, respectively. The
intermediates 19 decomposed already at 20 8C to yield the
allyl azides[22] 20 and 21, hence 19 d especially was always
present only in small proportions. We observed that at low
temperatures, at which the rearrangement of allyl azides
(equilibration of 20 and 21) had not yet begun, 20 b–d as well
as 21 b–d formed from 19 b–d. Consequently, 19 reacts not
only by cleavage of the two CN bonds of the threemembered ring, but also by cycloreversion of the fivemembered ring.
Highly strained 2,3-bridged 2H-azirines can also be
converted in the presence of ketenes, acyl isocyanates, or
nitrile oxides. We will report on these remarkable reactions
elsewhere.
Received: February 6, 2006
Revised: March 10, 2006
Published online: May 9, 2006
Scheme 5.
bridgehead azirine 3 l, which is not detectable by NMR
spectroscopy. The trapping product 18 l proves the particularly short-lived intermediate 3 l, in which the azirine unit is
further destabilized by the electron-withdrawing carbonyl
group.
The reaction of simple 2H-azirines with diazo compounds
to give allyl azides via 1,2,3-triazabicyclo[3.1.0]hex-2-enes
(compared with 19 in Table 3) has been known for more than
.
Keywords: azides · cycloaddition · dimerization ·
nitrogen heterocycles · strained molecules
[1] W. E. Billups, M. M. Haley, G.-A. Lee, Chem. Rev. 1989, 89,
1147 – 1159.
[2] Reviews on 2H-azirines: a) J. Backes in Houben-Weyl, Vol. E16c
(Ed.: D. Klamann), Thieme, Stuttgart, 1992, pp. 321 – 369; b) V.
Nair in The Chemistry of Heterocyclic Compounds, Small-Ring
Heterocycles, Vol. 42, Part 1 (Ed.: A. Hassner), Wiley, New York,
1983, pp. 215 – 332; c) W. H. Pearson, B. W.
Lian, S. C. Bergmeier in Comprehensive
Table 3: Treatment of 2,3-bridged 2H-azirines with diazomethane.
Heterocyclic Chemistry II, Vol. 1A (Ed.: A.
Padwa), Pergamon, New York, 1996, pp. 1 –
60; d) F. Palacios, A. N. Ochoa de Retana,
E. Martinez de Marigorta, J. M. de los Santos, Eur. J. Org. Chem. 2001, 2401 – 2414;
e) T. L. Gilchrist, Aldrichimica Acta 2001,
34, 51 – 55; f) K. M. L. Rai, A. Hassner in
Yield[a,b] of 20 + 21 [%]
Substrate 3
Max. yield[a]
Initial ratio
20/21 after
Advances in Strained and Interesting Organic
of 19 [%]
20/21[c]
equilibration
Molecules, Vol. 8 (Ed.: B. Halton), Jai,
n
R
X
Greenwich, 2000, pp. 187 – 257.
3b
6
H
CH2
89
89
4:1 (20 8C)
4:1
[3] For the ring strain in 2H-azirines, see: E.-U.
[d]
97
84 (62)
1:1 (20 8C)
2:1
3c
7
H
CH2
WIrthwein, T. HergenrJther, H. Quast, Eur.
<8
96 (78)[d]
2:1 (0 8C)
5:1
3d
8
H
CH2
J. Org. Chem. 2002, 1750 – 1755.
[d]
=
3j
6
Me
C O
86
85 (37)
1:0 (20 8C)
1:0
[4] a) A. Hassner, F. W. Fowler, J. Am. Chem.
Soc. 1968, 90, 2869 – 2875; b) A. Hassner,
[a] Yield based on 1H NMR standard. [b] Yield based on 3. [c] At low temperature. [d] Values in brackets
F. W. Fowler, Tetrahedron Lett. 1967, 8,
correspond to the yields of isolated products 20 + 21 based on the precursor 2.
1545 – 1548; c) B. Rose, D. Schollmeyer, H.
Meier, Liebigs Ann. 1997, 409 – 412.
[5] R. S. Atkinson, M. J. Grimshire, J. Chem.
[20]
forty years. The 1,3-dipolar cycloaddition of the starting
Soc. Perkin Trans. 1 1986, 1215 – 1224.
materials proceeds relatively slowly at room temperature
[6] a) K. M. L. Rai, A. Hassner in Comprehensive Heterocyclic
relative to the fragmentation of the postulated intermediate
Chemistry II, Vol. 1A (Ed.: A. Padwa), Elsevier, Oxford, 1996,
pp. 61 – 96, and references therein; b) J. Laue, G. Seitz, Liebigs
to yield the final products. Hence, short-lived 1,2,3Ann. 1996, 645 – 648; c) M. DrJgemIller, R. Jautelat, E. Wintertriazabicyclo[3.1.0]hex-2-enes, which were also discussed as
feldt, Angew. Chem. 1996, 108, 1669 – 1671; Angew. Chem. Int.
intermediates of the rearrangement of allyl azides,[21] could
Ed. Engl. 1996, 35, 1572 – 1574; d) M. DrJgemIller, T. Flessner,
not be proved spectroscopically until now.
R. Jautelat, U. Scholz, E. Winterfeldt, Eur. J. Org. Chem. 1998,
At 50 8C, the highly strained bridgehead azirines 3 b and
2811 – 2831; e) E. Haak, E. Winterfeldt, Synlett 2004, 1414 –
3 j react instantaneously with diazomethane by exo addition
1418; f) Y. Tamura, Y. Yoshimura, T. Nishimura, S. Kato, Y.
to give the tricyclic compounds 19 b and 19 j, respectively
Kita, Tetrahedron Lett. 1973, 14, 351 – 354; g) Y. Tamura, S. Kato,
4018
www.angewandte.org
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 4015 –4019
Angewandte
Chemie
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
Y. Yoshimura, T. Nishimura, Y. Kita, Chem. Pharm. Bull. 1974,
22, 1291 – 1296; h) S. Senda, K. Hirota, T. Asao, K. Maruhashi, J.
Am. Chem. Soc. 1978, 100, 7661 – 7664; i) D. S. Pearce, M. J.
Locke, H. W. Moore, J. Am. Chem. Soc. 1975, 97, 6181 – 6186;
j) M. Zaidlewicz, I. G. Uzarewicz, Heteroat. Chem. 1993, 4, 73 –
77.
W. E. Billups, G.-A. Lee, B. E. Arny, K. H. Whitmire, J. Am.
Chem. Soc. 1991, 113, 7980 – 7984.
Reviews on vinyl azides: a) K. Banert in Houben-Weyl, Vol. E15
(Eds.: H. Kropf, E. Schaumann), Thieme, Stuttgart, 1993,
pp. 818 – 875; b) A. Hassner in Azides and Nitrenes (Ed.:
E. F. V. Scriven), Academic Press, Orlando, 1984, pp. 35 – 76.
Treatment of 1-azido-2-iodocycloheptane with KOtBu followed
by separation by chromatography gave 2 c (31 %) as well as 3azidocycloheptene (25 %). Hassner6s route afforded 2 e (73 %
overall yield from cyclododecene) as a yellow oil.
A. Hassner, Acc. Chem. Res. 1971, 4, 9 – 16.
a) A. Hassner, F. W. Fowler, J. Org. Chem. 1968, 33, 2686 – 2691;
b) J. Schweng, E. Zbiral, Justus Liebigs Ann. Chem. 1978, 1089 –
1095.
From cyclohexene, we obtained by using Hassner6s route 3azidocyclohexene along with a portion of 2 b 1 %; see the
contrast to reference [13].
a) F. MIller, Dissertation, UniversitMt MInster, 1992; b) F.
MIller, J. Mattay, Angew. Chem. 1992, 104, 207 – 208; Angew.
Chem. Int. Ed. Engl. 1992, 31, 209 – 210; c) F. MIller, J. Mattay,
Chem. Ber. 1993, 126, 543 – 549.
C. E. Davis, J. L. Bailey, J. W. Lockner, R. M. Coates, J. Org.
Chem. 2003, 68, 75 – 82.
V. Nair, T. G. George, V. Sheeba, A. Augustine, L. Balagopal,
L. G. Nair, Synlett 2000, 1597 – 1598.
Our spectroscopic data of the four azirines 3 b–e (Table 1 and
Supporting Information) and the properties found for 3 b differ
very clearly from the statements in reference [13] (e.g., see the
data of 3 c and 3 e in reference [13c] for correct data of 3 d, see
also reference [4a,c]).
Alternative syntheses for 11 b, h and 12 a, b, c: a) R. K. Grasselli,
D. D. Suresh, D. R. Bridgeman, US Patent US4379925A, 1983
[Chem. Abstr. 1983, 99, 88 228]; b) D. G. Farnum, G. R. Carlson,
Synthesis 1972, 191 – 192; c) T. Kobayashi, S.-Y. Yamamoto, H.
Kato, Bull. Chem. Soc. Jpn. 1997, 70, 1193 – 1197; d) C. Herzig, J.
Gasteiger, Chem. Ber. 1981, 114, 2348 – 2354; e) T. Kobayashi, S.Y. Yamamoto, H. Kato, Bull. Chem. Soc. Jpn. 1997, 70, 1193 –
1197; f) H. E. Baumgarten, F. A. Bower, J. Am. Chem. Soc. 1954,
76, 4561 – 4564; g) J.-X. Chen, J.-P. Jiang, W.-X. Chen, T.-Y. Kao,
Heterocycles 1991, 32, 2339 – 2342.
For the addition of exactly one equivalent of HCN to 2methylene-2H-azirines, see: K. Banert, M. Hagedorn, E. KnJzinger, A. Becker, E.-U. WIrthwein, J. Am. Chem. Soc. 1994,
116, 60 – 62.
M. Mizuno, T. Shioiri, Tetrahedron Lett. 1999, 40, 7105 – 7108.
a) A. L. Logothetis, J. Org. Chem. 1964, 29, 3049 – 3052; b) V.
Nair, J. Org. Chem. 1968, 33, 2121 – 2123 und V. Nair, J. Org.
Chem. 1968, 33, 4316; c) T. C. Gallagher, R. C. Storr, Tetrahedron Lett. 1981, 22, 2909 – 2912; d) K. Banert, M. Hagedorn, C.
Liedtke, A. Melzer, C. SchJffler, Eur. J. Org. Chem. 2000, 257 –
267; e) T. M. V. D. Pinho e Melo, A. L. Cardoso, C. S. B. Gomes,
A. M. d6A. Rocha Gonsalves, Tetrahedron Lett. 2003, 44, 6313 –
6315.
A. Gagneux, S. Winstein, W. G. Young, J. Am. Chem. Soc. 1960,
82, 5956 – 5957.
Alternative syntheses for 20 b, d and 21 b: a) E. Maxa, E. Zbiral,
G. Schulz, E. Haslinger, Justus Liebigs Ann. Chem. 1975, 1705 –
1720; b) R. C. Hayward, G. H. Whitham, J. Chem. Soc. Perkin
Trans. 1 1975, 2267 – 2270.
Angew. Chem. Int. Ed. 2006, 45, 4015 –4019
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
4019
Документ
Категория
Без категории
Просмотров
0
Размер файла
136 Кб
Теги
synthesis, azirine, reaction, bridge, highly, strained
1/--страниц
Пожаловаться на содержимое документа